1. Field of the Invention
The present invention relates to a power amplifier applicable to a wireless communications system having improved linearity and degradation characteristics.
2. Description of the Related Art
In general, a wireless communications scheme is a digital modulation and demodulation scheme, and an appropriate scheme is employed in terms of the improvement of frequency usage efficiency. For example, a portable phone based on a code division multiple access (CDMA) scheme employs a quadrature phase shift keying (QPSK) scheme, and a wireless local area network (WLAN) following communications standard 802.11 set by the institute of electrical and electronics engineers (IEEE) employs a digital modulation scheme of orthogonal frequency division multiplexing (OFDM).
A wireless communications system employing a wireless communications scheme includes a power amplifier to amplify power of a transmission signal.
Here, a system requiring linear amplification requires a power amplifier having linearity to amplify a transmission signal without distortion. Here, linearity refers to characteristics in which power of an output signal is amplified at a uniform rate and a phase thereof is not changed even in the case that power of an input signal is changed.
An existing power amplifier provides a bias voltage generated in a bias circuit to a power amplifying element through resistance. Here, the bias circuit may include a temperature compensation function.
However, in the existing power amplifier, when a large signal is input, error vector magnitude (EVM) characteristics are not problematic but linearity thereof may be degraded, while when a small signal is input, EVM characteristics may be degraded.
The Related Art Document below relates to a power amplifier, which, however, does not disclose technical matters for improving linearity and characteristics degradation by discriminating between a large input signal and a small input signal.